Rome is a big, sprawling city, but the historic center is relatively small and easily navigated if one takes his bearings from the Tiber cutting through it.
The map we've made flies you between the top 5 attractions folks want to see. The first two, the Colosseum and the Vatican, are worth at least half a day, preferably an a guided tour. The remaining you can see on your own very easily. These are the Pantheon, the Trevi Fountain, and the Spanish Steps. The map loops, so if you miss something you'll see it again. There's a short description below the map.